Field devices as components of a process monitoring system are operated in technical facilities, for example for measuring the fill level, the limit or the pressure in a container, or for measuring the flow through a pipe. To this effect many of the field devices comprise sensors by means of which the actual measuring processes are carried out. The process monitoring system can comprise further field devices, which are, for example, used for forwarding and processing the acquired measured values to a central facility. Each of the field devices comprises a control by means of which, for example, a sensor can be operated, or by means of which results measured by the sensor can be further processed or forwarded.
For the supply of energy, each of the individual field devices is connected to a current source. Individual field devices can, for example, be connected to a power grid, for example by way of a line, or, for example, if they are situated in inaccessible locations, they can be coupled to a battery or an accumulator.
Although many measuring processes may need to be carried out only a few times each day, the field devices used for measuring may consume a relatively large amount of energy. If, moreover, the field devices are battery operated, spent batteries need to be exchanged regularly. This involves maintenance effort and expenditure.